Wrap-around cartons are normally formed on a high speed packaging machine which wraps a carton blank around the article or articles to be packaged and secures the ends of the blank in place. The ends of the blank typically overlap to form one of the panels of the carton, often the bottom panel. The overlapping panel flaps are held together by mechanical locking arrangements consisting of interlocking elements integral with the flaps. Although there are many different types of locking arrangements, it is necessary, particularly when the connected flaps comprise the bottom panel of the carton and are thus subjected to the full weight of the articles when the carton is lifted, to utilize a locking mechanism which prevents the panel flaps from opening under the stresses of normal use.
In one type of lock an integral tab in one of the flaps mates with a slot in the other flap. The tab has an arrowhead configuration wherein the back edge of the arrowhead engages with a surface of the second flap to prevent withdrawal of the tab. Mechanical fingers and other elements of the packaging machine position the flaps and insert the tab through the slot, all at a very high speed. This operation works well in connection with cartons containing articles which are spaced from each other a distance sufficient to enable the locking tabs to be located at points corresponding to the spaces. With such an arrangement the tabs can be pushed up into the interior of the carton when forming the interlock without encountering interference from the articles. Beverage container carriers are examples of cartons of this type. Even though the beverage bottles are adjacent one another, the circular shape of the bottle bottoms results in blank areas in the bottom panel unoccupied by the bottles. The locking elements can be located in these areas.
Even without spaces between the articles, there may be room in the interior of the package to permit tabs aligned with the articles to be secured in place. For example, if the package design permits some vertical movement of the articles there may be enough room to vertically insert the tabs when the articles and the partially formed carton are upside down, which often is the case when forming a carton around bottles.
When packaging articles which do not provide for blank unoccupied space in the bottom panel or which are held tightly in place in the carton with no room to move, there is no space available, or at best only extremely limited space, for the vertical insertion of locking tabs. This situation does not therefore permit the use of the usual vertically assembled locking tab arrangements designed to prevent the mechanical interlock from being pulled apart. The close proximity of the mechanical lock to the flat bottom of the articles largely permits only slight vertical tab movement during package assembly. An example of the type of package presenting this problem is a carton containing one or more tubs of food, such as butter. The tubs are tightly held in the carton with virtually no space between the tub and the top and bottom panels of the carton. The tubs extend substantially the full width of the carton, leaving no space for assembly of the usual type of vertically movable locking tabs.
It would be desirable to provide a locking mechanism which provides for the interlocking of adjacent overlapping panel flaps but which does not require vertical movement by an element of the packaging machine to insert the locking tabs. It would also be desirable to provide added protection in such an arrangement against withdrawal of the locking tabs.